It is desirable to determine the course of combustion in internal combustion engines, and various types of sensors have been developed therefor. The sensor described in the referenced application Ser. 06/214,481 is particularly arranged to sense irregular combustion events which may result in knocking. It is known to measure and determine and sense the combustion processes which occur in the combustion chamber of internal combustion engines during operation. It is desirable to sense as many physical parameters as possible. The temporal and spatial spread of the combustion process upon generation of a spark or injection of fuel is desirable, as well as exact sensing of ignition instant, determination and measuring of fuel injection processes, and the spread as well as spatial distribution of irregular combustion processes. The oxygen partial pressure also should be measured.
The referenced application describes a sensor in which, by optical sensing, combustion processes can be determined; it is particularly arranged to sense irregular combustion processes. Various other literature references referred to and summarized in the aforementioned referenced application describe additional sensing arrangements, for example a spectrometric process for investigating and checking the combustion of the fuel-air mixture in a Diesel engine. A quartz window is placed in the wall of the combustion chamber to permit spectrometric observation of the combustion event.
Oxygen partial pressure of combustion gases can be measured in various ways, for example by a potentiometric sensor or a polarographic sensor; potentiometric sensors operate similarly to a fuel cell by providing an output voltage if a reference oxygen partial pressure, for example as derived from oxygen in ambient air, differs from oxygen partial pressure within the sensed environment. Thus, if the environment contains a reducing atmosphere, an output voltage will be obtained which, upon change of the environment to an oxidizing condition, will drop suddenly to approximately null or zero output. Such sensors, also called lambda sensors, are used in connection with sensing the composition of exhaust gases from internal combustion (IC) engines. Other sensors operate in the polarographic mode, in which a limiting current will develop upon application of an external voltage to electrodes applied to the sensor element, the limiting current changing with change in oxygen content of the gas to be sensed. Typically, these sensors include an oxygen ion conductive solid electrolyte which has two boundary surfaces, one of them being exposed to a reference gas, for example ambient air which supplies oxygen, and the other to the gas to be tested for oxygen content. The solid electrolytes used are, customarily, ceramic elements, for example made of stabilized zirconium dioxide, supplied on their boundary surfaces with a gas permeable thin layer of electrode material, typically platinum. The sensor body, that is, the electrolyte with the electrodes applied thereto, may be in form of a closed tube having a sensing end exposed to the gas, in form of a disk, in which one surface is exposed to the gas to be tested, or may have other configuration. Such sensors are well known and described in the literature, see, for example, U.S. Pat. No. 3,841,987, FRIESE et al., and "Automotive Handbook", issued by Robert Bosch GmbH, pp. 275-277, section relating to exhaust gases.